1. Field of the Invention
The present invention relates to a pulse air jet generator mainly used for an air shower apparatus.
2. Description of the Prior Art
The entrance to a working room usually kept in a clean environment, such as a clean room or bio-clean room, is provided with an air shower apparatus for removing dust and/or bacteria adhering on cloths of persons who will enter the working room. The air shower apparatus is, for example, so configured as shown in FIG. 11, in which a box-type main case 82 is partitioned by a bulkhead 83 into an air shower chamber 84 which forms a passage penetrating the central portion of the main case 82, and air cleaning chambers 85 provided on both the sides of the air shower chamber 84. In such an air shower apparatus, an air sucked through a pre-filter 86 into each air cleaning chamber 85 reduced in pressure by a blower 87 is press-fed into an air chamber 88, and thereafter, by pressurizing the inside of the air chamber 88, the air cleaned by means of a high performance filter 89 in the air chamber 88 is jetted from air blowoff nozzles (punkah nozzles) 90 into the air shower chamber 84, to thereby remove dust and the like adhering on the cloth of a person 91 in the air shower chamber 84.
In such an air shower apparatus indicated by reference numeral 81 in FIG. 11, it is presumed that much of dust particles adhering on the cloth of the person 91 are substantially instantly removed therefrom by the jetted air. This is supported by an experiment made for examining a relationship between an air jetting time and a dust removing effect. Specifically, the experiment shows the tendency in which the dust removing effect is saturated after an elapse of several seconds since start of air jetting. As a result, to more increase the dust removing efficiency after air jetting, it is necessary for the person 91 in the air shower chamber 84 to turn around himself or beat the cloth by the hands.
The above-described fact also shows that air jetting performed intermittently is superior to air jetting performed stationarily or continuously in terms of improvement in dust removing effect. Specifically, a pulse air jet formed by intermittent or pulsative air jetting makes it possible to repeatedly reproduce impact forces each of which is generated at start of air jetting and which is effective for dust removal, and hence to give vibrations similar to those generated when the person repeatedly beats the cloth by the hands.
FIG. 12 is a graph showing results of an experiment, in which air jetting using the same jetting nozzle is performed continuously, and intermittently at three pattern cycles: (1) ON (jetted) for one second/OFF (stopped) for two seconds; (2) ON for one second/OFF for one second; and (3ON for one second/OFF for 0.5 second, and dust removing efficiencies (%) for dust particles having particle sizes of (0.3) .mu.m or more in the above conditions are measured. The experimental results show that the air jetting made intermittently at a short cycle is convenient for improving the dust removing efficiency.
The intermittent air jetting can be obtained by control of an air flow through opening/closing of a solenoid valve or damper; however, this method presents a problem that noise is enlarged with an increase in frequency of opening/closing actions and also the durability of the apparatus is degraded. Such a method causes another problem that provision of the solenoid valve or damper in each of a plurality of the air blowoff nozzles 90 opened toward the air shower chamber 84 complicates the entire configuration of the air shower apparatus and also increases the manufacturing cost and operating cost.